In a long term evolution (Long Term Evolution, hereinafter referred to as LTE) time division duplex (Time Division Duplex, hereinafter referred to as TDD) system, one uplink subframe needs to feed back response information of multiple downlink subframes. An acknowledgement (ACK, Acknowledgement) indicates that a UE correctly receives a corresponding transmission block transmitted on a corresponding physical downlink shared channel (Physical Downlink Shared Channel, hereinafter referred to as PDSCH). A negative acknowledgement (NACK, Negative Acknowledgement) indicates that a UE incorrectly receives a corresponding transmission block transmitted on a corresponding PDSCH. Discontinuous transmission (DTX, Discontinuous Transmission) indicates that a UE does not receive a corresponding transmission block transmitted on a corresponding PDSCH. In the LTE TDD system, modes for transmitting the response information of multiple downlink subframes in one uplink subframe may include a bundling mode and a multiplexing mode. In the LTE TDD system, a downlink assignment index (DAI, downlink assignment index) needs to be used to indicate scheduling information of the downlink subframes. The DAI is 2-bit information carried in downlink control information (DCI, downlink control information).
A DAI mechanism of the LTE TDD system is directly introduced into a long term evolution-advanced (Long Term Evolution-Advanced, LTE-A) system. Each carrier uses an independent DAI for counting, and bundled response information is transmitted on a physical uplink control channel (Physical Uplink Control Channel, hereinafter referred to as PUCCH) resource. The PUCCH resource is obtained according to a control channel element (CCE, Control Channel Element) with a minimum number on a physical downlink control channel (PDCCH, Physical Downlink Control Channel). The PDCCH is the PDCCH corresponding to a last downlink subframe received by the UE on multiple carriers. However, the PDCCH may not be a last PDCCH sent by the base station to the UE. The DAI cannot be used to detect whether another PDCCH is lost after the UE receives the PDCCH. Consequently, a mistake that the DTX is determined as an ACK may be caused, and the mistake can only be rectified by upper-layer retransmission. This prolongs a transmission delay of data sent by the base station to the UE, and reduces transmission efficiency.